The present invention relates to an image information-reading apparatus for reading image information from an original document placed on a document table.
In this technical field, an image information-reading apparatus that can read a color image is well known. This color image information-reading apparatus is connected to a thermal head color printer, for example, to copy the color image on an original document. Specifically, in the image-reading apparatus, the original document on the original table is optically scanned, thereby reading the color image information on the original document as optical color signals. The image-reading apparatus transmits these optical color signals to the printer. The color image information is printed out by the printer, using color ink on a color ink ribbon. The printing of the color image is carried out on the basis of the color information signals which designate the respective colors. In the printer, the thermal head thermally transfers the color ink onto a recording sheet on the basis of image information signals such that an image of one color is superposed on an image of another, thus copying the color image.
The color image information-reading apparatus is provided with a scanning unit. The scanning unit includes both an exposure lamp by which the original document is irradiated with light to expose it, and a photoelectric converting device (such as a solid-state image-sensing element) by which the light reflected from the original document is converted into electric signals. In the scanning unit, fiber lenses, which are arranged in an array, are located between the original table and the photoelectric converting device, to focus the reflected light on the photoelectric converting device. In the photoelectric converting device, a large number of elements corresponding to the respective colors are arranged adjacent to one another, and color components of the image on the original document are focused on the corresponding elements in accordance with the region determined by the array of the fibers lenses. The scanning unit is moved parallel to the original table, thus scanning the entire area of the original document.
If it is intended that an original produced by a halftone printing process, such as photographs in a newspaper, should be read and copied by the apparatus described above, moire noise may appear on the copy obtained. The moire noise occurs when the focal point of the fiber lenses is located exactly in the image-forming plane, in other words, when the image is formed most clearly in the plane. It is, therefore, considered that the moire noise is caused when the interval between the elements of the photoelectric converting device have an integral multiple relationship with the interval between the dots of the image. Incidentally, the moire noise becomes especially conspicuous when the image to be copied has a straight pattern or is yellow.